Interworking refers to the practice of connecting networks together. The term can refer to products, procedures, and technologies. Interworking as used here will refer to connecting networks together using different protocols, such as the International Telecommunications Union (ITU) recommendation H.323, “Packet-based multimedia communications systems,” (2003) and Session Initiation Protocol (SIP). SIP is an Internet Engineering Task Force (IETF) standard for initiating, modifying, and terminating an interactive user session that involves multimedia elements such as video, voice, instant messaging, online games, and virtual reality. SIP is set forth in the IETF Request for Comment (RFC) 3261, “Session Initiation Protocol,” (June 2002).
The IETF has a standard, RFC 4123, “H.323-SIP Interworking,” for interworking between these two protocols. This standard provides basic connections, but does not provide for fax connections in H.323, such as ITU's, “Procedures for real-time Group 3 facsimile communication over IP networks.” Generally, Group 3 facsimile communications use run-length encoding with a resolution 203×98 dots per inch, or 203×196 dpi for an 8½ inch by 11 inch document.